Disc brake devices in which the disc is pressed by two pistons via pads are conventionally known, as disclosed in Japanese Patent No. 2750862.
The caliper body disclosed in Japanese Patent No. 2750862 is equipped with movable large diameter and small diameter pistons, which are two pistons for pressing the disc plate via brake pads. The brake pads have pad set pins that are held movably in the axial direction of the disc plate and that position the disc plate in the peripheral direction. Braking torque from the brake pads is received by a pair of braking torque-receiving components.
The pad set pins are disposed in the longitudinal center of the brake pads.
The brake pads are composed of pads for sliding against the disc plate and back plates for supporting the pads.
When brake hydraulic pressure is produced and the disc plate is pressed by the large diameter and small diameter pistons via the brake pads to brake the disc plate, the brake pads move in the axial direction of the disc plate while sliding with the pad set pins and the braking torque-receiving components on the large diameter piston side.
Because virtually no braking torque acts on the pad set pin at this time, the pad set pin of the brake pads tends to move in the axial direction of the disc plate more than the braking torque-receiving component side of the brake pads, and the pad set pin side of the brake pads thus tends to undergo more wear than the braking torque-receiving component side of the brake pads; that is, uneven wear tends to develop.
In Japanese Patent No. 2750862, the large diameter piston is disposed near the braking torque-receiving component on the side where the disc plate comes out of the caliper body, and the small diameter piston is disposed on the side where the disc plate enters the caliper body, so that the pressing force with which the brake pads are pressed by the large diameter piston is greater than the pressing force with which the brake pads are pressed by the small diameter piston, suppressing uneven wear on the brake pads. However, the pad set pin and braking torque-receiving component are sometimes farther apart from each other, depending on the caliper body structure, and there is a need to prevent uneven wear on brake pads in these types of structures as well
In front wheel disc brake devices for two-wheeled vehicles where, for example, the large diameter piston of the two pistons is actuated by the brake lever on the right side of the handlebar and the small diameter piston is actuated by the brake lever on the left side of the handlebar or a brake pedal along with the piston of the rear wheel brake device, only one or the other of the large diameter piston or small diameter piston is sometimes actuated, which tends to cause uneven wear on a brake pad 11, necessitating some sort of action to prevent such uneven wear.